1. Field
The present disclosure relates to a resin-framed membrane-electrode assembly for a fuel cell and a method for manufacturing a resin-framed membrane-electrode assembly for a fuel cell.
2. Description of the Related Art
Typical solid polymer electrolyte fuel cells include solid polymer electrolyte membranes formed of polymer ion exchange membranes. A fuel cell includes a membrane-electrode assembly (MEA) in which an anode electrode is disposed on one side of a solid polymer electrolyte membrane and a cathode electrode is disposed on the other side of the solid polymer electrolyte membrane. The anode electrode and the cathode electrode each have a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon).
The membrane-electrode assembly is held between separators (bipolar plates) to form a fuel cell. A desired number of fuel cells are stacked, and the resulting fuel cell stack is used as an in-vehicle fuel cell stack, for example.
A membrane-electrode assembly may be configured as a so-called stepped MEA in which one of the gas diffusion layers has planar dimensions smaller than those of the solid polymer electrolyte membrane while the other gas diffusion layer has substantially the same planer dimensions as the solid polymer electrolyte membrane. In such a case, the MEA is combined with a resin frame member to decrease the amount of the relatively expensive solid polymer electrolyte membrane and protect the solid polymer electrolyte membrane which is a thin film having low strength. This type of MEA is called a resin-framed MEA.
An example of the resin-framed MEA is a membrane-electrode assembly disclosed in Japanese Unexamined Patent Application Publication No. 2007-66766. In this membrane-electrode assembly illustrated in FIG. 10, an anode catalyst layer 2a and an anode gas diffusion layer 2b both having the same outer dimensions as a membrane 1 are stacked on one surface of the membrane 1. A cathode catalyst layer 3a and a cathode gas diffusion layer 3b both having smaller outer dimensions than the membrane 1 are stacked on the other surface of the membrane 1. As a result, a stepped MEA 4 is configured.
The area of the anode gas diffusion layer 2b is set to be larger than the area of the cathode gas diffusion layer 3b. The membrane 1 has an outer perimeter portion on the cathode gas diffusion layer 3b side and the outer perimeter portion is bonded to a gasket structure 5 through a bonding portion 6.
According to Japanese Unexamined Patent Application Publication No. 2007-66766, the outer perimeter portion (flat surface) of the membrane 1 on the cathode gas diffusion layer 3b side is bonded to a flat surface of an inner perimeter thin portion 5a of the gasket structure 5 through the bonding portion 6 having a frame shape in a plan view.